[Err] ORA-00923: FROM keyword not found where expected 與rownum，ora-00923rownum

[Err] ORA-00923: FROM keyword not found where expected 與rownum，ora-00923rownum
關於oracle的nownum

如果我想查詢表的全部資訊,並且前面加上行號,sql如下

select  ROWNUM,* from tableA

會報下面的錯誤

[Err] ORA-00923: FROM keyword not found where expected

得給表加上別名

SELECT  ROWNUM,a.* ROWNUM FROM tableA   a

為什麼需要這樣,我還沒深入學習,大家誰知道,請告訴我